Abstract: Abstract: This paper studied the selection and modification of the main pumps of the second pumping station of Huai'an by using CFD. The study analyzed the operation status of the main pumps and confirmed the necessity of reinforcement of the main pumps of the second pumping station of Huai'an. Selecting the main pumps for the second pumping station of Huai'an was carried out based on its operation data over these years, and the excellent hydraulic model of TJ05-ZL-02 was chosen. The hub ratio of the hydraulic model TJ05-ZL-02 is 0.4, while the original hub ratio of the second pumping station of Huai'an is 0.4667. Therefore, the hub ratio of the chosen hydraulic model must be modified. At the same time, to meet the requirements of diversion, drainage engineering of the second pumping station of Huai'an ensured that the pump model modified has the similar performance with the chosen hydraulic model, reduce the coefficient of flow and decrease the head of the high efficient area. First of all, this paper analyzed the influence of the main parameters including cascades dense degree and blade angle of each section on the hydraulic performance of axial-flow pumps. Which controlling the change of directions of the blade hydraulic performance. And use CFD to verify the hydraulic performance of the axial-flow pump when parameters changes. then decided the final retrofit design program. The feasibility of retrofitting program has been demonstrated through the numerical simulation of comparing the axial-flow pumps device before and after modification. Numerical simulation of the pump device adopts the standard k-ε model, and calculated the six flow point at 280, 300, 320, 340, 360 and 380 L/s, respectively. Finally, the experimental studies of the model pump showed that, model test performance curve trend was consistent with the numerical performance curve. According to flow-head curve , there is a little deviation in small flow area, and the flow-efficiency curve fit well, the performance of numerical simulation and experimental study has been mutual authentication. The head is in the range of 3.5 to 4.5 m, and the flow of 300 to 350 L/s after modification, which will fully meet the requirements of diversion, drainage and irrigation of the second pumping station of Huai'an for current and future. After modifications, the efficiency of axial-flow pumps device was over 70%, while the efficiency of the second pumping station of Huai'an initially was 68%, with nearly 20% increased, which play a huge role in increasing diversion performance and reducing cost. And the research shows that hub ratio of modified pump increasing may decline the overall performance of axial-flow pump, which indicates that there is the most optimal hub ratio for a specific speed of axial-flow pump,. It has very important significance for the optimal design of axial-flow pump hydraulic model and the large-scale pumping station renovation.